Enzymes

2.2.3 Syllabus Objectives

• Define the term: enzymes

• State the nature, folded shape & functions of

enzymes.

• Explain the role of enzymes in plants and

animals including role in metabolism

• Explain the effects of pH & temperature on

enzyme activity.

• State the procedure and advantages of Bio-

processing.

• State the use of Bio-processing. 2

• Most reactions take place in a number of

steps which need to be carefully controlled

if the cell is to function properly

• Enzymes are the most important

controllers of cellular reactions

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Catalysts

• Catalysts speed up reactions without themselves

being involved in the reaction

• Enzymes are catalysts made of protein they

speed up a reaction without being used up

themselves in the reaction

• Because enzymes are made in living things they

are called biological (or organic catalysts)

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• We learned in the chapter on food that

proteins are made when amino acids join

together

• The function of a protein is decided not

only by the sequence of amino acids but

also by the way the protein folds

• Most enzymes are globular proteins

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Learning Check

• What is an Enzyme?

• What are catalysts?

• To what group of bio-molecules do

enzymes belong?

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How enzymes work

• Enzymes are not flat they have a 3D

structure

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• Each enzyme has its own

specific shape that will

only “fit” the molecule that

the enzyme is designed

to work on

• If the enzyme that breaks

starch into glucose meets

a fat molecule it will not fit

it and will not be able to

work on it

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Learning Check

• Why is the shape of an enzyme important?

• Are enzymes flat, 3D or 2D in shape?

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Enzyme Action

• The substance that an enzyme acts on is

its substrate

• The substance(s) that the enzyme forms is

called the product(s)

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A Catabolic enzyme

• Amylase converts starch to maltose

• Catabolic as it breaks a big molecule into

a smaller one

• It is produced by saliva glands in mouth

and by the pancreas

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An Anabolic Enzyme

• DNA Polymerase forms and repairs DNA

• Anabolic as it coverts simpler molecules

into more complex molecules

• Found in almost all living things

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Consider This

• Amylase is an enzyme found in saliva. It breaks

starch molecules into smaller maltose molecules

• What is the substrate?

• What is the product?

• Will amylase break fats into fatty acids +

glycerol? Why?

• Is this an example of a catabolic or an anabolic

reaction? Why?

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And This

• DNA Polymerase is an enzyme that builds DNA using tiny molecules in our cells

• What is the substrate?

• What is the product?

• Will amylase build keratin out of peptides? Why?

• Is this an example of a catabolic or an anabolic reaction? Why?

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• Enzymes work because they have the correct shape to fit the substrate

• They have a complex 3 dimensional shape to fit the substrate

• When enzymes and their substrates meet and come together they form an Enzyme/Substrate complex

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Learning Check

• What is meant by a substrate?

• What is the unit formed when an enzyme

combines with its substrate called?

• Give an example of an anabolic reaction

• Give an example of a catabolic reaction

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• Enzyme Reactions are reversible

• Like a key can open or close a lock

enzymes can make reactions go in either

direction

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• In the following example the enzyme can

break molecule X into Y+Z but it can also

combine Y+Z to form X

X Y + Z

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Learning Check

• Can enzyme reactions be reversed?

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Naming Enzymes

• Enzymes are named by adding the suffix

ase to the name of their substrate

Eg.

• Enzyme that acts on Amylose (starch) is

called amylase

• Enzymes that act on proteins are called

proteases

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Learning Check

• Can you think of a name for enzymes that

act on Lipids?

• Amazingly enough they are called

Lipases!

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Inhibitors

• Inhibitors attach to enzymes and destroy

their shape

• When this happens the enzymes are said

to be denatured

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Nerve Gases

• The nerve gases we hear of terrorists

using are often inhibitors that attach to

enzymes involved in our nerve

transmissions

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Poisoning people the old fashioned

way!

• Cyanide denatures an enzyme involved in

respiration

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Beneficial Inhibitors

• Insecticides affect enzymes in insects

causing their death

• Drugs can affect enzymes involved in pain

causing the pain to stop

• Antibiotics can affect enzymes in bacteria

causing the bacteria to die

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Learning Check

• What is an inhibitor?

• How do inhibitors work?

• Can you give an example of a harmful

inhibitor?

• Can you give an example of a beneficial

inhibitor?

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Enzymes at work!

• Enzymes work best in certain conditions

Factors that affect enzymes include

• Temperature

• pH

• Substrate concentration

• Enzyme concentration

• We will be examining these in experiments

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Temperature

• At very low temperatures ice forms, liquids

become solids and enzymes can’t work

• As temperature increases molecules start

to move and bump into each other causing

the rate of reaction to increase

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• Human enzymes work best at body temperature (37°C)

• Plant Enzymes work best at 20-30 °C

• Above certain temperatures enzymes start to lose their shape the rate of reaction falls

• When the shape is fully lost the enzyme is said to be denatured this is usually a permanent condition

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pH

• pH scale goes from 0 -14

• 0-7 is acidic

• 7-14 is basic (or alkaline)

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• Enzymes work over a very narrow pH

• Most enzymes work at pH 6-8

• Outside this they lose shape and get denatured

• The optimum or best ph is usually pH 7

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An Exception!

• Is our stomach acid or basic?

• Do you think there are enzymes in our

stomach?

• Pepsin is an enzyme in the stomach that

works best at pH 2!

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Learning Check

• What factors affect enzyme action?

• What is the best temperature for (a)

human enzymes and (b) plant enzymes

• What is meant by pH?

• Do enzymes work over a narrow or wide

pH range?

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Immobilised Enzymes

• Bio-processing is the use of enzyme

controlled reactions to produce a product

• Bio-processing can be used to produce a

vast range of products such as cheeses,

beer, antibiotics, vaccines, methane gas,

food flavours, vitamins and perfumes

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• Traditionally micro-organisms such as

bacteria and yeast were used but since

the 1900’s and especially since the 1950’s

enzymes are being used

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• If enzymes are used freely dissolved in a vessel

it can be very wasteful as they are lost at the

end of the process

• To prevent this problem enzymes are often

immobilised or fixed

• This means they are attached to each other or

an inert substance and can be used repeatedly

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Learning Check

• What is bio-processing?

• What type of organisms are uasually used

in bio-processing?

• Why is bio-processing advantageous?

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How to immobilise enzymes

• Physical methods

• Adsorption where enzymes are physically attached to inactive supports such as glass beads or ceramics

• Enclosed by a membrane when enzymes are kept within a membrane

• Trapped in a gel, sodium alginate is commonly used this allows substrates in and products out

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• Chemical Methods

• Bonded to a support enzymes

chemically bonded to a support such as

glass beads or ceramics

• Bonded to each other Enzymes are

chemically bonded to each other

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Learning Check

• Describe 2 physical methods of

immobilising enzymes

• Describe 2 chemical methods of

immobilising enzymes

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Advantages of Immobilised

Enzymes

• Efficiency of enzyme is not affected

• Immobilised enzymes can be easily recovered from the product so you can get a pure sample of product easily

• Immobilised enzymes can be reused this cuts costs

• Enzymes frequently become more stable when immobilised

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Uses of Immobilised Enzymes

• Immobilised glucose isomerase converts

glucose to fructose which is used to

sweeten drinks

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• Penicillin acylase changes the structure of

penicillin to make more antibiotics that will

fight a wider range of bacteria

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• Lactase converts lactose to sweeter

sugars glucose and galactose which are

then used by food manufacturers

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Learning check

• What are the advantages of immobilising

enzymes?

• Can you name 3 things immobilised

enzymes are used for?

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END

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